The present disclosure is generally directed, in various embodiments, to silane-phenol compounds, crosslinked siloxane-phenolic protective overcoat layers comprising the hydralysates and condensates of the silane-phenol compounds and hydroxymethylated hole transport compounds, and electrophotographic imaging members comprising such crosslinked siloxane-phenolic protective overcoat layers.
In the art of xerography, or electrophotographic printing/copying, an electrophotographic imaging member such as photoreceptor is electrostatically charged. For optimal image production, the photoreceptor should be uniformly charged across its entire surface. The photoreceptor is then exposed to a light pattern of an input image to selectively discharge the surface of the photoreceptor in accordance with the image. The resulting pattern of charged and discharged areas on the photoreceptor forms an electrostatic charge pattern (i.e., a latent image) conforming to the input image. The latent image is developed by contacting it with finely divided electrostatically attractable powder called toner. Toner is held on the image areas by electrostatic force. The toner image may then be transferred to a substrate or support member, and the image is then affixed to the substrate or support member by a fusing process to form a permanent image thereon. After transfer, excess toner left on the photoreceptor is cleaned from its surface, and residual charge is erased from the photoreceptor.
Electrophotographic photoreceptors can be provided in a number of forms. For example, the photoreceptors can be a homogeneous layer of a single material, such as vitreous selenium, or it can be a composite layer containing a photoconductive layer and another material. In addition, the photoreceptor can be layered. Current layered photoreceptors generally have at least a flexible substrate support layer and two active layers. These active layers generally include a charge generating layer containing a light absorbing material, and a charge transport layer containing electron donor molecules. These layers can be in any order, and sometimes can be combined in a single or a mixed layer. The flexible substrate support layer can be formed of a conductive material. Alternatively, a conductive layer can be formed on top of a nonconductive flexible substrate support layer.
A photoreceptor can be in a rigid drum configuration or in a flexible belt configuration. The belt can be either seamless or seamed.
Typical photoreceptor drums comprise a charge transport layer and a charge generating layer coated over a rigid conducting substrate support drum. For example, many advanced imaging systems are based on the use of small diameter photoreceptor drums. The use of small diameter drums places a premium on photoreceptor life. A major factor limiting photoreceptor life in copiers and printers is wear. The use of small diameter drum photoreceptors exacerbates the wear problem because, for example, 3 to 10 revolutions are required to image a single letter size page. Multiple revolutions of a small diameter drum photoreceptor to reproduce a single letter size page can require up to 1 million cycles from the photoreceptor drum to obtain 100,000 prints, a desirable goal for commercial systems.
For low volume copiers and printers, bias charging rolls (BCR) are desirable because little or no ozone is produced during image cycling. However, the micro corona generated by the BCR during charging, damages the photoreceptor, resulting in rapid wear of the imaging surface, e.g., the exposed surface of the charge transport layer. For example, wear rates can be as high as about 16 μm per 100,000 imaging cycles. Similar problems are encountered with bias transfer roll (BTR) systems. One approach to achieving longer photoreceptor drum life is to form a protective overcoat on the imaging surface, e.g. the charge transporting layer of a photoreceptor. This overcoat layer must satisfy many requirements, including transporting holes, resisting image deletion, resisting wear, avoidance of perturbation of underlying layers during coating, and etc.
For flexible photoreceptor belts, the charge transport layer and charge generating layer are coated on top of a flexible substrate support layer. To ensure that the photoreceptor belts exhibit sufficient flatness, an anticurl backing layer can be coated onto the back side of the flexible substrate support layer to counteract upward curling and ensure photoreceptor flatness. The flexible photoreceptor belts are repeatedly cycled to achieve high speed imaging. As a result of this repetitive cycling, the outermost layer of the photoreceptor experiences a high degree of frictional contact with other machine subsystem components used to clean and/or prepare the photoreceptor for imaging during each cycle. When repeatedly subjected to cyclic mechanical interactions against the machine subsystem components, photoreceptor belts can experience severe frictional wear at the outermost organic photoreceptor layer surface that can greatly reduce the useful life of the photoreceptor. Ultimately, the resulting wear impairs photoreceptor performance and thus image quality.
In U.S. Pat. No. 5,702,854 to Schank et al. issued Dec. 30, 1998, an electrophotographic imaging member is disclosed including a supporting substrate coated with at least a charge generating layer, a charge transport layer and an overcoating layer. The overcoating layer comprises a dihydroxy arylamine dissolved or molecularly dispersed in a crosslinked polyamide matrix. The overcoating layer is formed by crosslinking a crosslinkable coating composition including a polyamide containing methoxy methyl groups attached to amide nitrogen atoms, a crosslinking catalyst and a dihydroxy amine, and heating the coating to crosslink the polyamide. The electrophotographic imaging member may be imaged in a process involving uniformly charging the imaging member, exposing the imaging member with activating radiation in image configuration to form an electrostatic latent image, developing the latent image with toner particles to form a toner image, and transferring the toner image to a receiving member.
In U.S. Pat. No. 5,681,679 issued to Schank, et al., a flexible electrophotographic imaging member is disclosed including a supporting substrate and a resilient combination of at least one photoconductive layer and an overcoat layer, the at least one photoconductive layer comprising a hole transporting arylamine siloxane polymer and the overcoat comprising a crosslinked polyamide doped with a dihydroxy amine. This imaging member may be utilized in an imaging process including forming an electrostatic latent image on the imaging member, depositing toner particles on the imaging member in conformance with the latent image to form a toner image, and transferring the toner image to a receiving member.
Yuh et al. have disclosed an electrophotographic imaging member in U.S. Pat. No. 5,709,974 issued on Jan. 20, 1998. The electrophotographic imaging member includes a charge generating layer, a charge transport layer and an overcoat layer. The transport layer includes a charge transporting aromatic diamine molecule in a polystyrene matrix and the overcoat layer includes a hole transporting hydroxy arylamine compound having at least two hydroxy functional groups and a polyamide film forming binder capable of forming hydrogen bonds with the hydroxy functional groups of the hydroxy arylamine compound.
In U.S. Pat. No. 5,368,967 issued to Schank et al., an electrophotographic imaging member is disclosed comprising a substrate, a charge generating layer, a charge transport layer, and an overcoat layer comprising a small molecule hole transporting arylamine having at least two hydroxy functional groups, a hydroxy or multihydroxy triphenyl methane and a polyamide film forming binder capable of forming hydrogen bonds with the hydroxy functional groups the hydroxy arylamine and hydroxy or multihydroxy triphenyl methane. This overcoat layer may be fabricated using an alcohol solvent. This electrophotographic imaging member may be utilized in an electrophotographic imaging process. Specific materials including Elvamide polyamide and N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine and bis-[2-methyl-4-(N-2-hydroxyethyl-N-ethyl-aminophenyl)]-phenylmethane are disclosed in this patent.
Crosslinked siloxane overcoat layers have demonstrated good potentials for extrinsic life extension of, for example, organic photoreceptors. Owing to its crosslinked siloxane structure, the overcoat layer offers excellent abrasive, scratching and marring resistance. However, several shortcomings are also associated with crosslinked siloxane-containing overcoat layers. In particular, in electrophotographic photoreceptors in which the overcoat layer is the crosslinked siloxane material, image deletion occurs when the environmental contaminants around the charging device in the xerographic engine interact with the overcoat. Furthermore, another shortcoming associated with the siloxane-containing overcoat layers is the high torque required to rotate the coated photoreceptor against a cleaning blade. In addition, because the crosslinked siloxane overcoat layers are typically prepared by sol-gel processes, shrinkage of the applied layer occurs, which strains the resulting materials. Although attempts have been made to solve these problems by modifying various component materials, such modifications typically present trade-offs in terms of improving one property while deteriorating another property. The main causes are believed to be poor micromechanical properties and sensitive to corona effluence.
As such, new protective overcoat designs are needed to manufacture an electrophotographic imaging member such as photoreceptor with improved properties such as image deletion resistance, cleanability, low friction, among others.